1. Field of the Invention
The present invention generally relates to a positioning system. More specifically, the present invention relates to a positioning system, a positioning terminal, an information provision device, a positioning method, a control program for a positioning system, and a computer-readable recording medium for recording a control program for a positioning system.
2. Background Information
A GPS (Global Positioning System) for positioning utilizing position information satellites has been widely used. In order to receive position-related signals transmitted from GPS satellites and to calculate the position of the reception point, since it is necessary to perform calculations using massive amounts of such as acquisition of GPS satellites, decoding of position-related signals, and calculation of pseudo range, a high-end CPU (Central Processing Unit) is required. This requirement becomes an obstacle to miniaturization and price-reduction in GPS receiving devices.
In Japanese Patent Application Publication No. 2000-131415 (FIG. 1 etc.), a GPS positioning system is disclosed in which part of the functions necessary for positioning calculations is provided by a server, information obtained by a GPS receiving terminal is transmitted to the server, and position calculation is performed by the server is disclosed. Such a positioning system is called a server-assist system. Japanese Patent Application Publication No. 2000-131415
In the invention of Japanese Patent Application Publication No. 2000-131415 (FIG. 1 etc.), since the GPS receiving terminal is arranged to transmit all information obtained from the GPS satellites to the server without any particular differentiation, the transmitted information includes unnecessary information for position calculation. Thus, an extra load is applied to the server which can be problematic.
Accordingly, in Japanese Patent Application Publication No. 2003-139841 (FIG. 3 etc.), in a portable terminal with built-in GPS used in a server-assist positioning system, a configuration is disclosed in which information to be transmitted to a server is selected according to an acquisition result of GPS satellites for reducing a load on the server. Japanese Patent Application Publication No. 2003-139841 is hereby incorporated by reference.
In the GPS system, essentially, if it is possible that four GPS satellites are acquired, three-dimensional positioning can be performed. However, even if four GPS satellites can be acquired, depending on the arrangement of those acquired GPS satellites, sometimes DOP (Dilution of Precision) becomes larger and positioning can not be performed.
In the portable terminal with built-in GPS in the Publication No. 2003-139841, information to be transmitted to the server is selected using elevation of the acquired GPS satellites or electric field intensity as reference. Accordingly, there is a problem in that the server performs position calculations and CPU time is wasted even when the GPS satellite arrangement is not preferable and position calculation is impossible.
In view of the above, it will be apparent to those skilled in the art from this disclosure that there exists a need for an improved a positioning system, a positioning terminal, an information provision device, a positioning method, a control program for a positioning system, and a computer-readable recording medium for recording a control program for a positioning system. This invention addresses this need in the art as well as other needs, which will become apparent to those skilled in the art from this disclosure.